package acwing._2LanQiao._1Recursion;

import java.util.Scanner;

/**
 * @Project : ProgrammingExercises
 * @Package : ACWing._2LanQiao._1_1Recursion
 * @File : Q1208.java
 * @Author : WangRuoyu
 * @Date : 2023/3/13 14:06
 */
public class Q1208 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String s =scan.nextLine();
        String p =scan.nextLine();
        StringBuilder ss = new StringBuilder(s);

        int res = 0;

        for (int i = 0; i < s.length() - 1; ++i) {
            if (ss.charAt(i) != p.charAt(i)) {
                char ch = (char) ('*' + 'o' - ss.charAt(i));
                ss.replace(i, i + 1, String.valueOf(ch));
                ch = (char) ('*' + 'o' - ss.charAt(i + 1));
                ss.replace(i + 1, i + 2, String.valueOf(ch));
                res++;
            }
        }

        System.out.println(res);
    }
}
